class_docstr: Represents a sub-structure of a OverlayGraph.
  
  Often, we want to find structures within a graph, such as branches and
  sequences, to assist with graph layout for users.
  
  An OverlayStructure represents such a structure. It is typically used
  in conjunction with OverlayGraph.collapse_structures() to parse a graph.
code: def __contains__(self, item):
      return OverlayNode.as_name(item) in [
          n.name for n in self.children
      ]
  
imports: from collections import defaultdict
  import numpy
  import tensorflow
label_desc: Use image node_id 2 for calling the OverlayStructure obj's underlying member method code with example usage: obj.__contains__(item) and returns: unknown